1515,
what acft do you fly? on the boeings that i flew B744 (GE & PW), B734 (CFM) and now the B777 (RR Trent), they are all 'flat-rated' to ISA+15__°C. just as mutt said, they produce max thrust at ISA+15°C. you can try this out. when the OAT < 30°C, try entering a SEL TEMP (derate) of less than 30°C, you will noticed then TO thrust will NOT reduce beyond that of 30°C.
SR